Hello,
These dry scabs could have been due to
lice or dandruff.Check whether your son’s scalp
is infested with liceor dandruff. You may be able to see the lice or nits by parting your child's hair into small sections and checking for lice and nits on the scalp.
If there is lice infestation,then pls shampoo the hair with anti lice shampoos which are available over the counter.
Hope it helps.Take care and pls do keep me posted on how your son is doing or if you have any additional doubts.